This work examines positive solutions of systems of inequalities ±∆pu ≥ ρ(x)f (u), in Ω, where p = (p1, ..., pk), pi > 1 and ∆p is the diagonal-matrix diag(∆p1 , ..., ∆pk ), ∆pi is the pi-Laplace operator, Ω is an arbitrary domain (bounded or not) in RN (N ≥ 2), u = (u1, ..., uk)T and f = (f1, ..., fk)T are vector-valued functions and ρ(x) is a nonnegative function in Ω which is locally bounded. Using a maximum principle-based argument we provide explicit estimates on positive solutions u at each point x ∈ Ω, and as applications we find Liouville type results in unbounded domains such as RN, exterior domains or generally unbounded domains with the property that supx∈Ω dist(x, ∂Ω) = ∞, for various nonlinearities f and weights ρ. We also give explicit upper bounds on extremal parameters of related nonlinear multi-parameter eigenvalue problems in bounded domains.